Work carried out during the first granting period has demonstrated that the edema associated with experimental heart failure produced by thoracic caval constriction in the dog is associated with an elevated water intake and increased plasma vasopressin concentration. Water restriction alleviated the edema. The major objective of the proposed study is to evaluate the importance of increased thirst and retention of water in the edema of congestive cardiac failure. The effect of a possible increase in salt appetite will also be studied. The experiments will be carried out in dogs with implanted atrial and arterial cannulae and with flow probes around the root of the aorta. Fluid and electrolyte balances will be measured, and manipulations such as thoracic caval constriction, mitral stenosis and pulmonary stenosis carried out, and the edema which should develop will be followed. Measurements will be made of plasma renin activity, angiotensin II, vasopressin, ACTH and aldosterone. The effect of graded water and/or salt restriction on the edema and cardiac pperformance will be studied, as will the effect of blockade of the renin/angiotensin system. A parallel series of experiments will also be carried out on two-kidney Goldblatt hypertension. These studies should elucidate the role of disordered water metabolism in the edema of congestive cardiac failure.